The present invention relates to a lighting circuit device for controlling the on-off of a lamp (e.g., a head lamp) mounted in an automobile.
A discharge-lamp lighting circuit device for an automobile of the sort mentioned above is designed to control the lighting of a discharge lamp for use as an head lamp. In the discharge-lamp lighting circuit device, DC voltage is boosted to a desired DC voltage, which is converted to AC voltage in a square wave form, and the discharge lamp is lighted by superposing a starting pulse on the AC voltage. After the discharge lamp is lighted, the quantity of light is regulated by controlling the operation of a booster circuit according to a signal indicating the current and voltage to be applied to the discharge lamp. While the current and voltage, and the battery voltage for the discharge lamp is being monitored, moreover, the control operation is stopped when any abnormality is detected. In order for the operation like this to be performed, a specific IC together with a discharge-lamp lighting circuit is provided in the automotive discharge-lamp lighting circuit device. In other words, a circuit built up in this specific IC is used for controlling the operation of the booster circuit and for performing a fail-safe operation when any abnormality occurs.
The present patent applicant considers letting a discharge-lamp lighting circuit device for an automobile have a leveling function for regulating light distribution in a head lamp, for example. More specifically, a leveling device for regulating light distribution in a head lamp as a second circuit device is electrically connected to the discharge-lamp lighting circuit device as a first circuit device, and sensor information from height sensors and a speed sensor is fed to the discharge-lamp lighting circuit device. Information on light distribution for the leveling device is created in this discharge-lamp lighting circuit device and the information on light distribution thus created therein is sent to the leveling device. In this case, it may be considered possible to incorporate the function of generating the information on light distribution for the leveling device into a specific IC but this question will have to be dealt with by changing the specific IC within the discharge-lamp lighting circuit device according to the car type because suspension hardness and the like make the information on light distribution variable with the car type.